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February 1983 Notes 119
<br />is "spreading southward", perhaps as a result of the proliferation of reservoirs, and that the influx
<br />of these predators may have impacts on zooplankton populations in southern waters.
<br />Leptodora kindtii was encountered in the lower Mississippi River near St. Francisville, Louisi-
<br />ana, as early as June 6, 1973 (Bryan et al., Appendix E in Environ. Rept., Constr. Permit Stage,
<br />River Bend Station Units 1 and 2, Gulf States Utilities Co., Baton Rouge, Louisiana, 1974). Bin-
<br />ford (M.S. thesis, Louisiana State Univ., Baton Rouge, Louisiana, 1975) took L. kindtii in the
<br />Atchafalaya river (a Mississippi River distributary) near the mouth of Bayou Cherie, St. Martin
<br />Par., Louisiana, in March 1974. The latter locality lies roughly at the latitude of New Orleans (ca.
<br />30° S), or about 300 km south of Lake Texoma, from which the southernmost formally-published
<br />records are available (Holt et al., Southwestern Nat. 23:686-688, 1978).
<br />Both southern Louisiana records for L. kindtii were obtained soon after initiation of sampling
<br />with 1-m diameter, 0.505-mm mesh conical townets in the respective study areas (April 3, 1973 in
<br />the Mississippi; September 27, 1973 in the Atchafalaya). The question whether or not L. kindtii
<br />was always present will remain moot, for Conner and Bryan (Prot Ann. Conf. SE Assoc, Game
<br />Fish Commrs. 28:429-441, 1975) found no reference to any previous use in the lower Mississippi-
<br />/Atchafalaya Rivers of meter-nets or other gear suitable for sampling macrozooplankton. The
<br />fine-meshed, relatively small-mouthed nets and bottle samples used in most limnological studies
<br />prior to the 1970's are notoriously selective against larger, strong-swimming zooplankters
<br />(Schindler, J. Fish. Res. Bd. Canada 26:1948-1955, 1969). At least some of the recent discoveries of
<br />L. kindtii in southwestern reservoirs were apparently associated with larval fish sampling.
<br />Coarse-mesh plankton sampling has continued through the present on a monthly or more fre-
<br />quent basis at the St. Francisville, Louisiana, site, as well as irregularly in various parts of the
<br />Atchafalaya Basin. Leptodora kindtii has been encountered at least once in each year since 1973,
<br />but without indication of gradually increasing frequency of occurrence or catches/effort. For
<br />example, at one Mississippi River Station where effort was comparable, mean annual
<br />numbers/100 m3 were: 1973 (3.3); 1974 (4.4); 1975 (0.9); 1976 (12.6); and 1977 (0.2). Specimens have
<br />been taken as early as March and as late as November, but in most years L. kindtii has been most
<br />common and abundant in June and July; individual sample estimates (based on impeller-type
<br />flowmeter readings) for early summer collections in 1973-77 ranged from 3 to 25/100 m'. Speci-
<br />mens ranging from about 2 to 10 mm (total length) have been observed, indicating that at least
<br />some reproduction occurs locally; most smaller specimens (<3 mm) have appeared in summer and
<br />early autumn.-JOHN V. CONNER, School of Forestry and Wildlife Management, AND C. FRED
<br />BRYAN, Louisiana Cooperative Fishery Research Unit, Louisiana State Univ., Baton Rouge, LA
<br />70803.
<br />COLORADO SQUAWFISH, PTYCHOCHEILUS LUCIUS (CYPRINIDAE), WITH A
<br />CHANNEL CATFISH, ICTALURUS PUNCTATUS (ICTALURIDAE), LODGED IN ITS
<br />THROAT.-The Colorado squawfish (Ptychocheilus lucius) is a large cyprinid endemic to the
<br />Colorado River basin. Historically, it was widely distributed in the Colorado River and its major
<br />tributaries (Minckley, Fishes of Arizona, Arizona Game and Fish Dept., 293 pp., 1973), but habitat
<br />modification has resulted in its decline. The species was listed as Endangered by the U.S. Fish and
<br />Wildlife Service (Federal Register 39:1175, 1974).
<br />One factor in its decline that is frequently suggested is the ingestion of introduced channel cat-
<br />fish (Ictalurus punctatus). Undocumented reports exist of Colorado squawfish found dead with
<br />channel catfish lodged in the esophagus (Seethaler, M.S. thesis, Utah State Univ., 1978; Vanicek
<br />and Kramer, Trans. Am. Fish. Soc., 98:193-208, 1969). Presumably the squawfish died from suffo-
<br />cation or starvation.
<br />In December, 1974 an adult Colorado squawfish (550 mm TL) with a channel catfish (120 mm
<br />TL) lodged in its esophagus was collected by trammel net at Sand Wash on the Green River, 348
<br />km upstream from its mouth. The catfish was headfirst, with the pectoral fins locked out and
<br />lodged in the esophageal wall immediately posterior to the gill arches. The channel catfish was
<br />contained completely within the mouth of the Colorado squawfish and was not attached to the
<br />trammel net. Therefore, it is unlikely that the channel catfish was caught in the net before it was
<br />ingested by the Colorado squawfish.
<br />In the Colorado River Basin universities, consulting companies, and state and federal agencies
<br />have spent considerable time on the rivers and collected relatively large numbers of Colorado
<br />squawfish. For example, the U.S. Fish and Wildlife Service collected 466 subadult and adult Colo-
<br />rado squawfish (>200 mm TL) in 1979-81 and found none with ictalurids lodged in their throats
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